Carotenoids are natural pigments that are responsible for many of yellow, orange and red colors seen in living organisms. Carotenoids are widely distributed in nature and have, in various living systems, two main biological functions. They serve as light-harvesting pigments in photosynthesis and they protect against photo-oxidative damages. Carotenoids have important commercial uses as coloring agents in the food industry since they are non toxic. The flesh, feathers or eggs of fish and bird assume the color of the dietary carotenoid provided and thus carotenoids are frequently used in dietary additives for poultry and in aquaculture. Moreover, carotenoids protect against damaging generated by near ultra violet (UV) radiations and in addition, have an anti-oxidative function. For all these reasons, carotenoids are important nutrious, cosmetic and pharmaceutical products and have a high economic value.
Over 600 different carotenoids have been described from carotenogenic organisms found among bacteria, yeast, fungi and plants. Currently only two of them, β-carotene and astaxanthin are commercially produced in microorganisms. β-carotene is obtained from algae and astaxanthin is produced in Phaffia yeast strain.
However, in the case of cultured products from Phaffia yeast, a great deal of expense is incurred for the gathering and extraction of astaxanthin, because said yeast has rigid cell walls and produces astaxanthin in a low yield. Also, in case of the cultured product of the green alga Haematococcus, not only the location for collecting sunlight, but an investment of a culturing apparatus for supplying an artificial light is required in order to supply light which is essential to the synthesis of carotenoids. For these reasons, carotenoids produced from biological source presently is inferior to that obtained by organic synthetic methods due to the cost. Organic synthetic methods, however, result in by-products. Thus, with a view to use them as a feed for fishes and shellfishes and an additive to foods, the products obtained by these organic synthetic methods are unacceptable due to the consumer's preference for natural products.
So, it is then desired to have genes that play a role in the biosynthesis of carotenoids, to produce carotenoids from microorganisms by introducing a gene or a gene cluster. No problem of by-products as a contaminants would thus be incurred. Moreover it would be considered not difficult to increase the production amount of carotenoids with gene manipulation to a level higher than that accomplished by the organic synthetic methods.